NORTH ADAMS — Composer Julia Wolfe is used to writing music for ensembles of all shapes and sizes. But she’d never before written a score that called for clogging — nor wooden bones, banjo, or mountain dulcimer.

But “Steel Hammer,” her epic explosion and reconstruction of the folk ballad “John Henry,” called for a real down-home feel. Aptly, the musicians she works with tend to have meticulous conservatory training but catholic sensibilities when it comes to musical style.

“The music is genuinely inside of me, so it’s about the sensibility and the body energy of the folk music and the organization and architecture of a composition. It’s about how these worlds fit together in my mind,” she reflects.

In its deliberate intermingling of folk traditions and what we might call art music, “Steel Hammer,” a finalist for the 2010 Pulitzer Prize in music, is very much in keeping with the other offerings at the 12th Bang on a Can Summer Festival, which begins Wednesday at Mass MoCA. (One of the festival centerpieces, it will be performed on July 27.)

The 18-day event is a wild mishmash of offerings from some leading practitioners of the music sometimes oxymoronically described as contemporary classical, but more frequently known by a rather neutral-sounding title: new music.

Bang On A Can Summer Festival

Led by Wolfe and fellow composers Michael Gordon and David Lang, Bang on a Can is a New York-based collective that, over 26 years, has likely done more than any other to promote and promulgate the next generation of new-music composers and performers.

Its summer festival is both an intensive training program for a crop of highly advanced students (known as fellows), who study and perform with Bang on a Can regulars, and a smorgasbord of listening options for the musically adventurous.

‘We want to expand everyone’s idea of what music-making is, of what the possibilities are.’

A festival-capping, six-hour marathon of contemporary music (almost all of which is authored, this year, by living composers) provides an uncommon depth of variety. A surfeit of cello fellows in 2012 prompted a performance of Steve Reich’s “Cello Counterpoint,” scored for one live musician and seven pre-recorded parts — or, in this case, eight cellos. Pieces by Led Zeppelin and John Zorn also got the all-cello treatment.

This year's adventure includes the festival’s first-ever quartet of acoustic basses, and a 20-piece chamber orchestra playing arrangements of tunes by Aphex Twin, the purveyor of progressive electronic music. Guest conductor Alan Pierson, cofounder of the new-music ensemble Alarm Will Sound, leads that bit.

“We’re drawing the line over to artists who are working in more popular forms of music, and getting our fellows used to that idea,” explains Gordon. “We want to expand everyone’s idea of what music-making is, of what the possibilities are. The idea that you’re coming out of conservatory and you’re going to play classical music for the rest of your life is not the path that everyone is going to be taking.”

Aphex Twin’s work is “very complex and very rhythmically challenging,” Gordon says. “The ideas from the classical avant-garde and what used to be thought of as the fringe of experimental popular music are much closer than one might think.”

Though some new music can sound esoteric and theory-drenched to the uninitiated listener, this crew is particularly interested in confounding expectations. They want to tease out the accessibility in conceptually ambitious work.

A sense of whimsy permeates the festival. Each day at lunchtime, students have the chance to pick any gallery in the museum to stage pop-up recitals. Audiences are a mix of festival diehards and museum patrons who might stumble upon a series of performances as they stroll the galleries. These are followed by a more formal series of gallery recitals by Bang on a Can faculty, daily at 4:30 p.m. On any given night, the music-making might even continue at the pub across the street, where one official concert — an evening of Latin music — is scheduled for July 24. There’s even a free show at nearby Windsor Lake.

“The idea is not: Here is this big piece of capital-a Art that we’re going to perform at you and bash you over the head with it and you’re just going to take it,” explains Brandon Randall-Myers, a guitar fellow last year who returns this summer to focus on composing. “It feels like it’s much more about creating a space for dialogue, where people can appreciate the music for what it is. And if they don’t like it, they can just leave.”

The egalitarian ethos extends to Wolfe’s “John Henry” project, where one might find a metaphor about Bang on a Can itself, taking new music out of the academy in an implicit argument for its enduring relevance.

“I actually love the inaccuracy of it. That’s part of what's so delightful,” she says of the hundreds of different versions of the ballad, with differing claims on every matter of fact from the hero’s name to his place of birth. “So many groups have claimed him for their own — the unions, the communists, the African-American community. There’s just so many people who want to own him. He belongs to such a wide group of people.”